Comparative Techno-Economic Assessment of Solar Thermal HumidificationDehumidification and PV-Driven Reverse Osmosis for Inland Brackish Water Desalination

Abstract

Inland brackish-water desalination requires systems that deliver reliable freshwater under variable solar conditions while minimizing electrical energy demand, levelized cost of water (LCOW), and brine-management constraints. This study presents a 12-month pilot-scale comparison of solar thermal humidification–dehumidification (HDH) and photovoltaic-driven reverse osmosis (PV-RO) in an inland highsolar environment. Under baseline brackish groundwater conditions, PV-RO proved superior as a primary desalination pathway. PV-RO achieved a 57.1% higher area-normalized freshwater yield (28.9 vs. 18.4 L m⁻² day⁻¹) and reduced specific electrical energy consumption by 44.7% (6.8 vs. 12.3 kWh m⁻³). Product water quality was also stronger for PV-RO, with 98.3% TDS removal compared with 95.8% for HDH. Utilizing a capacity-scaled framework for a 1,000 m² deployment, PV-RO delivered a lower projected LCOW (1.38 USD m⁻³) compared to HDH (2.61 USD m⁻³). However, rigorous thermodynamic closure—including an empirical HDH Gain-Output Ratio (GOR) of 2.06—and solution-diffusion modeling (J_w=A(ΔP-Δπ) redefine this performance hierarchy at elevated salinities. Sensitivity mapping defines a quantitative tipping point: scaling-induced degradation of RO permeability drives its LCOW above the thermodynamically stable HDH baseline of 2.61 USD m⁻³. Consequently, this study proposes a synergistic inland deployment architecture, utilizing PV-RO for primary recovery and reserving HDH as a salinity-resilient, secondary brine concentrator to achieve decentralized Zero Liquid Discharge (ZLD).